In recent years, with advances in technology, the requirement of image quality becomes higher, and, therefore, it is necessary to improve the brightness or other parameters to increase the image quality. For this reason, to provide a light element having higher efficiency (e.g. higher brightness, purer color, longer lifetime) to a projection device is necessary. The laser diode is the better selection to satisfy the requirement of the light element, and the application of the laser diode is revealed in U.S. Pat. Nos. 7,502,176 and 6,665,331. In addition, in order to enable the projection device to satisfy the requirement of the high brightness, a light module with dozens of the laser diodes is provided in prior art.
FIG. 1A is an exploded schematic diagram of a conventional laser diode module. FIG. 1B is an assembled schematic diagram of the conventional laser diode module of FIG. 1A. Referring to FIGS. 1A and 1B, the conventional laser diode module 100 includes a lens bracket 120, a lens holder 140, a laser diode holder 160, a plurality of laser diodes 180, and a plurality of lenses 190. The laser diode holder 160 has a plurality of mounting holes 162 for receiving the laser diodes 180 therein. The lens holder 140 is disposed on the laser diode holder 160 and has a plurality of holding holes 142 for receiving the lenses 190 therein. Each lens 190 is disposed to correspond to one of the laser diodes 180. The lens bracket 120 is disposed on the lens holder 140 and has a plurality of locating holes 122 for fixing the lenses 190.
The machining tolerances are generated while manufacturing the components of the conventional laser diode module 100. The accumulation of these machining tolerances results in poor performance of the conventional laser diode module 100. Specifically, the machining tolerances include the diameter tolerance of each locating hole 122 of the lens bracket 120, the spacing tolerance between each two neighboring locating holes 122, the diameter tolerance of each holding hole 142 of the lens holder 140, the spacing tolerance between each two neighboring holding holes 142, the diameter tolerance of each mounting hole 162 of the laser diode holder 160, and the spacing tolerance between each two neighboring mounting holes 162. In addition, the bending deformation of the lens bracket 120, the lens holder 140 and the laser diode holder 160 may occur in the assembly process or in the production process, and thus the flatness of the lens bracket 120, the lens holder 140 and the laser diode holder 160 is reduced. Therefore, the spacing between the lens bracket 120 and the lens holder 140 is not uniform. Similarly, the spacing between the lens holder 140 and the laser diode holder 160 is not uniform. For these reasons, in the conventional laser diode module 100, it is hard to precisely align the optical axis of each laser diode 180 with the optical axis of the corresponding lens 190. Therefore, the concentricity accuracy between each laser diode 180 and the corresponding lens 190 is poor, and thus the illuminating efficiency of the conventional laser diode module 100 is reduced.
In addition, the temperature of the laser diodes 180 is enhanced when the laser diodes 180 work, and therefore the laser diodes 180 cannot be fixed by adhesive, but must be gripped and fixed by the laser diode holder 160 and the lens holder 140. However, the size of the laser diode holder 160 is too large and thus is easily out of shape, so it is difficult to let the flatness of the laser diode holder 160 satisfy a predetermined standard. Therefore, some of the laser diodes 180 cannot be gripped and fixed, and the laser diodes 180 and the lenses 190 cannot be precisely assembled. Furthermore, the lens bracket 120, the lens holder 140 and the laser diode holder 160 are formed with many holes such as the locating holes 122, the holding holes 142 and the mounting holes 162, so the structure strength of the lens bracket 120, the lens holder 140 and the laser diode holder 160 is relatively frail. Therefore, the lens bracket 120, the lens holder 140 and the laser diode holder 160 are easily bent and deformed because of the high temperature generated in the machining process and the pressure generated from clamping the laser diodes 180 and the lenses 190, and thus the laser diodes 180 and the lenses 190 cannot be precisely assembled, thereby reducing the illuminating efficiency of the conventional laser diode module 100.
In addition, in the conventional laser diode module 100, the relative position of each laser diode 180 and its corresponding lens 190 is fixed by the lens bracket 120, the lens holder 140 and the laser diode holder 160. During the assembly process, dozens of the laser diodes 180 and the lens 190 are placed in the lens holder 140 and the laser diode holder 160. However, after the assembly process, if the relatively position between one of the lenses 190 and its corresponding laser diode 180 is deviated, the laser diode module 100 must be reassembled. During the reassembly process, all the elements must be realigned. Therefore, the assembly process of the laser diode module 100 is complicated and has poor accuracy.
If the numbers of the laser diodes 180 are less, the assembly deviation can be ignored. However, when large numbers of the laser diodes 180 are used to increase the brightness of the projection device, the accumulation of the above-mentioned tolerances will greatly exceed the permissible range. Therefore, the conventional laser diode module 100 is adverse to be applied to the high brightness projection device.